Effect of protein overfeeding on energy expenditure measured in a metabolic chamber.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 25733634 · doi:10.3945/ajcn.114.091769
What was done
Twenty-five men and women were randomized to consume approximately 40% excess energy for 56 days from diets containing 5%, 15%, or 25% protein (with excess energy provided as fat in the low-protein group). Twenty-four-hour energy expenditure (24EE) and sleeping energy expenditure (SleepEE) were measured in a metabolic chamber on days 1, 14, and 56 of overfeeding, as well as on day 57 during a return to baseline diet. Skeletal muscle biopsy specimens were collected for metabolic and molecular markers.
What was found
In the low-protein group (excess fat), 24EE and SleepEE did not increase on day 1 of overfeeding, and SleepEE remained unchanged across the study. In groups receiving excess protein, acute increases in 24EE and SleepEE correlated with protein intake (r = 0.50, P = 0.02). Over 8 weeks across all three groups, 24EE correlated with protein intake (r = 0.60, P = 0.004) but not with total energy intake (r = 0.16, P = 0.70). Observed 24EE exceeded predicted values on day 1 (P <= 0.05), day 14 (P = 0.0001), and day 56 (P = 0.0007). Protein and fat oxidation were reciprocally related, and change in fat mass was not related to change in energy expenditure.
Why it matters
This study demonstrates that the acute and sustained rise in metabolic rate during overfeeding is driven specifically by protein intake rather than total caloric excess or fat accumulation.
Limits
The sample size is small (n = 25 split across three arms). The abstract does not provide absolute energy expenditure values in calories, baseline participant demographics, or the specific findings from the skeletal muscle biopsies.
Cited by
- contradicts The human body cannot store excess protein, converting surplus intake into fat.